IMPORTANCE: Several studies suggest that the apolipoprotein E (APOE) epsilon4 allele modulates cerebrospinal fluid (CSF) levels of beta-amyloid 42 (Abeta42). Whether this effect is secondary to the association of the APOE epsilon4 allele with cortical Abeta deposition or whether APOE epsilon4 directly influences CSF levels of Abeta42 independently of Abeta pathology remains unknown. OBJECTIVE: To